Software Types

• System Software
• Real Time Software
• Business Software
• Scientific Software
• Embedded Software

Software Reuse

Software Reuse, also called code reuse, is the use of existing software, or software knowledge, to build new software. Ad hoc reuse has been practiced from the earliest days of programming. Programmers have always reused sections of code, templates, functions, and procedures. Software reuse as a recognized area of study in software engineering, however, dates only from 1968 when Douglas McIlroy of Bell Laboratories proposed basing the software industry on reusable components.

Reusable software, or software knowledge items, are called reusable assets. Assets may be designs, requirements, test cases, architectures, etc.

Perhaps the most well known reusable asset is code. Code reuse is the idea that a partial or complete computer program written at one time can be, should be, or is being used in another program written at a later time. The reuse of programming code is a common technique which attempts to save time and energy by reducing redundant work.

A very common example of code reuse is the technique of using a software library. Many common operations, such as converting information among different well-known formats, accessing external storage, interfacing with external programs, or manipulating information (numbers, words, names, locations, dates, etc.) in common ways, are needed by many different programs. Authors of new programs can use the code in a software library to perform these tasks, instead of “re-inventing the wheel”, by writing fully new code directly in a program to perform an operation. Library implementations often have the benefit of being well-tested, and covering unusual or arcane cases. Disadvantages include the inability to tweak details which may affect performance or the desired output, and the time and cost of acquiring, learning, and configuring the library.

The software library is a good example of abstraction. Programmers may decide to create internal abstractions so that certain parts of their program can be re-used, or may create custom libraries for their own use.

For newly written code to use a piece of existing code, some kind of interface, or means of communication, must be defined. These commonly include a “call” or use of a subroutine, object, class, or prototype. In organizations, such practices are formalized and standardized by software product line engineering.

The general practice of using a prior version of an extant program as a starting point for the next version, is also a form of code reuse.

Some code reuse involves simply copying some or all of the code from an existing program into a new one.

Many researchers have worked to make reuse faster, easier, more systematic, and an integral part of the normal process of programming. These are some of the main goals behind the invention of object-oriented programming, which became one of the most common forms of formalized reuse. A somewhat later invention is generic programming.

Another, newer means is to use software “generators”, programs which can create new programs of a certain type, based on a set of parameters that users choose. Fields of study about such systems are generative programming and metaprogramming.

From Wikipedia, the free encyclopedia

Software Engineering

Software Engineering is the application of a systematic, disciplined, quantifiable approach to the development, operation, and maintenance of software. The term software engineering was popularized during the 1968 NATO Software Engineering Conference (held in Garmisch, Germany) by its chairman F.L. Bauer, and has been in widespread use since. The discipline of software engineering encompasses knowledge, tools, and methods for defining software requirements, and performing software design, software construction, software testing, and software maintenance tasks. Software engineering also draws on knowledge from fields such as computer engineering, computer science, management, mathematics, project management, quality management, software ergonomics, and systems engineering.

As of 2004, the U. S. Bureau of Labor Statistics counts 760,840 software engineers holding jobs in the U.S.; for comparison, in the U.S. there are some 1.4 million practitioners employed in all other engineering disciplines combined. There are estimated to be about 1.5 million practitioners in the E.U., Asia, and elsewhere[citation needed]. SE pioneers include Barry Boehm, Fred Brooks, C. A. R. Hoare, and David Parnas.

Nature
David Parnas has said that software engineering is, in fact, a form of engineering. Steve McConnell has said that it is not, but that it should be. Donald Knuth has said that programming is an art.

The U.S. Bureau of Labor Statistics classifies computer software engineers as a subcategory of “computer specialists”, along with occupations such as computer scientist, programmer, and network administrator. The BLS classifies all other engineering disciplines, including computer hardware engineers, as “engineers”.

The U.K. has seen the alignment of the Information Technology Professional and the Engineering Professionals. Software engineering in Canada has seen some contests in the courts over the use of the title “Software Engineer”

Definition
Typical formal definitions of software engineering are

“the application of a systematic, disciplined, quantifiable approach to the development, operation, and maintenance of software”. “an engineering discipline that is concerned with all aspects of software production” “the establishment and use of sound engineering principles in order to economically obtain software that is reliable and works efficiently on real machines”

Other meanings
As Dijkstra pointed out, the terms software engineering and software engineer have, at times, also been used (or misused) in a much wider sense, particularly in America.The term has been used less formally:

as the informal contemporary term for the broad range of activities that was formerly called programming and systems analysis; as the broad term for all aspects of the practice of computer programming, as opposed to the theory of computer programming, which is called computer science; as the term embodying the advocacy of a specific approach to computer programming, one that urges that it be treated as an engineering discipline rather than an art or a craft, and advocates the codification of recommended practices in the form of software engineering methodologies.

Purpose
Software is often found in products and situations where very high reliability is expected, even under demanding conditions, such as monitoring and controlling nuclear power plants, or keeping a modern airliner aloft Such applications contain millions of lines of code, making them comparable in complexity to the most complex modern machines. For example, a modern airliner has several million physical parts (and the space shuttle about ten million parts), while the software for such an airliner can run to 4 million lines of code. See also List of software engineering topics (thematic) and List of software engineering topics (alphabetical).

From Wikipedia, the free encyclopedia